Maccaris advice is good, he has some more on sizing under one of his seal listings:
https://www.airrifleheadquarters.com...485/834669.htm
Also good advice. It is very easy to go too far in sizing, looking for the optimal "sliding fit"- and then, after some shooting, the seal ends up undersized.
I prefer a quite high lathe speed when sizing, and using a quite coarse sand paper (180-240 grit). I use it dry, but move it around to avoid clogging.
Try to keep the shape of sealing edges intact.